The goal of this study is to use the Activa Primary Cell + Sensing (PC+S) device to study Latent Field Potential (LFP) in the brains of people with Treatment Resistant Depression (TRD) before and during active stimulation. The ultimate goal is to understand the neural network that causes TRD and the changes that DBS cause in that network that results in the antidepressant effects.

Major depressive disorder is a common disease. For many people, conventional treatments such as antidepressants are very helpful in relieving the symptoms of this condition. But as many as 30% of patients with depression have less than a full response or become resistant to conventional treatments. When treatment resistance develops, the depression becomes a chronic disease with a very significant burden of morbidity and mortality. The reasons that some patients develop Treatment Resistant Depression (TRD) are not known. One current theory for depression is that it results from the dysfunction of a network of regions in the brain and that in treatment resistant patients the network is permanently stuck in the dysfunctional state. We have been investigating an experimental treatment for treatment resistant depression (TRD), based on this network theory known as subcallosal deep brain stimulation (SCC DBS). This treatment involves placement of electrodes in a specific region of the brain (subcallosal cingulate cortex, area 25) and then stimulating that area with electricity, which resets the regulation of the network resulting in a significant antidepressant response. While still experimental our results suggest this may eventually be a useful treatment for some patients with TRD. The experiment described in this application is to use a new DBS device that can record the electrical activity in the brain around the site of stimulation. The electrical activity is known as Latent Field Potential (LFP) and is a reflection of the activity if the neural network. The new DBS device is an experimental device that has not been approved by the Food and Drug Administration (FDA), but allows for simultaneous recording of LFP while stimulation is being delivered. The device is manufactured by Medtronics and is known as Activa Primary Cell + Sensing(PC+S), but because it can be used to record the brain electrical activity it is also known as "the Brain Radio". The Brain Radio is based on an approved device commonly used for DBS for other conditions that has the added sensor capacity. The stimulation system is identical to that in the approved device. The goal of this investigation is to use the Brain Radio to study LFP in the brains of people with TRD before and during active stimulation. The ultimate goal is to understand the neural network that causes TRD and the changes that DBS cause in that network that results in the antidepressant effects. We will recruit 10 patients with advanced TRD and implant them with the Brain Radio system. The recording system will be to record LFP over 3 years, while patients receive stimulation. A brief discontinuation study will be conducted after 6 months of stimulation when the device will be turned off and patterns of LFP changes will be recorded. All LFP measures will be correlated with the primary clinical response outcome metric, the Hamilton Depression Rating Scale. The knowledge gained with this experiment will be invaluable to understanding the basic pathology of depression and the antidepressant response. This is a unique, first in humans test of this device and as such the results are expected to impact our understanding of depression at a fundamental basis.

Deep brain stimulation of the subcallosal cingulate white matter (SCC25 DBS) has been investigated as a new interventional strategy for treatment resistant depression (TRD). In addition to growing evidence of long-term antidepressant efficacy with chronic stimulation, immediate changes in mood, attention, and psychomotor speed during intra-operative testing have been repeatedly observed. These acute, electrode contact-specific behavioral effects have successfully guided selection of the optimal contact for chronic DBS. The presence of intraoperative behavioral effects is often predictive of long-term outcome. It is clear that sustained high frequency stimulation appears to be required to maintain the antidepressant response long-term, as discontinuation even after several years of remission is associated with deterioration and return of depression symptoms over several weeks. Imaging studies examining effects of chronic SCC25 DBS using positron emission tomography (PET) demonstrate changes in blood flow and metabolism both in the vicinity of the DBS target, and remotely in frontal cortex, ventral striatum, hypothalamus and amygdala/hippocampus. These findings, combined with more recent diffusion tensor imaging (DTI) studies, provide evidence of the anatomical and functional extent of regional changes mediating antidepressant effects of DBS over time [5-6].

Brain changes mediating the observed intra-operative behavioral changes or discontinuation-precipitated relapse are unknown. To date, none of the studies have been able to address explicit mechanisms of DBS for TRD at the neuronal level, during chronic stimulation. It is possible to make measurements of neuronal activity with available recording systems only during intraoperative testing. Given that TRD requires chronic stimulation to achieve full remission, characterization of changes in neural activity throughout the duration of stimulation and development of therapeutic response will be invaluable in further developing and refining this treatment modality. Furthermore, tracking of neural changes and their behavioral correlates with chronic stimulation and controlled discontinuation would allow characterization of physiologic markers for potential use as feedback signals for further treatment development and optimization.

This set of new experiments will build on past experience of utilizing SCC25 DBS in patients with TRD to explore potential neural correlates of antidepressant response. This will be done using the ActivaPC+S, which is a prototype DBS system developed by Medtronic that combines conventional DBS brain electrodes and pulse generator with a sensing device that can chronically read, record and download the electrical brain activity known as Local Field Potential (LFP) at the brain area surrounding the DBS electrode. These recordings can be downloaded from the implanted device with an external antenna device similar to the device used to control the pulse generator. Given the ability to record LFP locally in the brain and to transmit this information to a receiving station the ActivaPC+S device is referred to as the "Brain Radio".

The ActivaPC+S, "Brain Radio" device is an experimental system currently not approved by the FDA. This device is based on the ActivaPC system, which has FDA approval for use in Parkinson's disease, Essential Tremor and has Humanitarian Device Exemption (HDE) for Dystonia. The ActivaPC also has an HDE for use in intractable Obsessive Compulsive Disorder (OCD). The Brain Radio has sensing technology in addition to the standard stimulation capacity of the approved device that allows for real time recording of LFP in the anatomical location of the electrode both during active stimulation and when stimulation is off. As such this is a very powerful research tool that will facilitate investigation of the neuronal changes associated with antidepressant response to chronic DBS. This will be the first ever use of this unique, cutting edge system in human patients with treatment resistant depression and has the potential to provide unprecedented insight into the fundamental neuronal processes that underlie depressive illness and antidepressant response.

Hypothesis 1: Aberrant oscillations in the SCC-prefrontal circuitry are present in TRD patients. SCC25 DBS exerts its therapeutic effects by altering these network dynamics. Behavioral improvements in TRD patients treated with SCC25 DBS will correlate with discernible LFP changes at specific DBS electrode contacts, both acutely and chronically.

Hypothesis 2: Stable maintenance of stimulation-induced LFP changes is required for sustained antidepressant response, with loss of these changes heralding impending depression relapse.

This study will test these hypotheses in 10 TRD patients via recording LFPs with the ActivaPC+S system throughout the course of chronic SCC25 DBS. Measures of SCC LFP oscillatory activity will be correlated with clinical measures of antidepressant response and with scalp EEG signals.

OBJECTIVES Experiment #1: To quantify electrophysiological changes, behavioral correlates and EEG changes in the month following implantation when the stimulator is turned OFF.

Experiment #1A: To characterize the LFP changes for 48 hours post op in response to the brief, acute stimulation the patient receives during the implantation procedure Experiment #1B: To characterize the changes in LFP patterns in the month after implantation and to establish a baseline before chronic stimulation is initiated. The Activa PC+S system will be utilized to record LFP during this phase of the protocol.

Experiment #2: The stimulator will be turned on 1 month after implantation. This experiment will occur on the day of stimulation initiation. Clinical data will be recorded and LFP changes will be captured by the Activa PC+S system and scalp EEG. The stimulator will be cycled through a series of different frequency and current settings while LFPs are recorded.

Experiments #3: To quantify LFP changes in response to chronic high frequency SCC25 stimulation and to correlate change patterns with long-term antidepressant response and EEG patterns. Stimulation will be initiated one month after implantation and maintained chronically for the subsequent 6 months. Clinical assessments, LFP and scalp EEG will be routinely recorded during this 6-month period.

Experiment #4: To quantify LFP changes when the stimulation is briefly stopped (1 week) after 6 months of chronic stimulation. Correlation will be made between LFP, clinical/ symptomatic changes and EEG patterns.

Experiment #5: To quantify LFP changes over the extended period of exposure to chronic high frequency SCC25 stimulation. Clinical response and EEG patterns will be recorded every 6 months and compared to LFP over the battery life of the ActivaPC+S system; currently estimated at 3 to 5 years after initiation of stimulation.

The primary clinical outcome metric is the Hamilton Depression Rating Scale.

Inclusion Criteria:

• Ability to provide written informed consent.
• Agrees to relocate to the Atlanta Metro region for the duration of the acute phase of the investigation (approximately 8-10 months) and to return regularly for clinical and research assessments
• Current Major Depressive Episode (MDE), either Major Depressive Disorder single episode or recurrent type
• Current depressive episode of at least two years duration or a history of more than 4 lifetime depressive episodes
• Minimum score at study entry of 20 on the 17-item Hamilton Depression Rating Scale (HDRS-17)
• Average pre-operative HDRS-17 score of 20 or greater (averaged over four weekly pre-surgical evaluations during the four weeks prior to surgery) and an average pre-operative HDRS-17 score no more than 30% lower than the baseline screening HDRS-17 score
• A maximum Global Assessment of Functioning of 50 or less
• Failure to respond to a minimum of four different antidepressant treatments, including at least three medications from at least three different drug classes, evidence-based psychotherapy or electroconvulsive therapy (ECT) administered at adequate doses and duration during the current episode
• Failure or intolerance of an adequate course of electroconvulsive therapy (ECT) during any episode
• On stable antidepressant medication
• Have an established outpatient psychiatrist and be willing to sign a written release to allow study investigators to give and receive information from this psychiatrist

Exclusion Criteria:

• Inability/ refusal to sign written informed consent
• Refusal or inability to relocate to Atlanta Metro region for acute phase of protocol or to return for regular assessments in long term follow up
• Inability to tolerate general anesthesia
• Significant cerebrovascular risk factors or a previous stroke, documented major head trauma or neurological disorder
• Other currently active clinically significant Axis I psychiatric diagnosis including bipolar disorder, schizophrenia, panic disorder, obsessive-compulsive disorder, generalized anxiety disorder or post-traumatic stress disorder
• Current psychotic symptoms
• Evidence of global cognitive impairment
• Substance abuse or dependence not in full, sustained remission
• Active suicidal ideation with intent; suicide attempt within the last six months; more than three suicide attempts within the last two years
• Pregnancy or plan to become pregnant during the study period
• General contraindications for DBS surgery (cardiac pacemaker/defibrillator or other implanted devices)
• Inability or unwillingness to comply with long-term follow-up
• History of intolerance to neural stimulation of any area of the body
• Participation in another drug, device or biologics trial within the preceding 30 days prior to initial screening
• Conditions requiring repeated MRI scans
• Conditions requiring diathermy
• Conditions requiring anticoagulant medication
• Terminal illness associated with expected survival of <12 months